Method for splitting carbon fiber tow

ABSTRACT

Provided is a method for splitting a carbon fiber tow, which comprises heating a carbon fiber tow sized with a first sizing material to soften the first sizing material and form a spread carbon fiber tow; passing the spread carbon fiber tow through at least one splitter and corresponding cutter to obtain multiple carbon fiber strands spaced apart; and sizing the carbon fiber strands with a second sizing material. With the method, multiple small carbon fiber tows having better tensile strength and/or modulus than the commercially available small carbon fiber tow products can be obtained. Products made of the small carbon fiber tows obtained by the present invention are lighter but stronger, and the production cost is relatively reduced. The present invention also achieves the purpose of energy saving and carbon reduction.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for producing a carbon fibertow; more particularly, to a method for producing a small carbon fibertow having high tensile strength and/or high modulus which is notcommercially offered for sale yet.

2. Description of the Prior Arts

High-performance fibers refer to fibers that have exceptionalcharacteristics compared to ordinary fibers. High-performance fibershave high tensile strength, high modulus, good heat resistance, goodcorrosion resistance, good wear resistance, good incombustibility, andhigh chemical stability. So the high-performance fibers are important ingeneral industries (e.g. wind power generation, new energy vehicles, 3Cproducts, sporting goods, and the like) and defense industries (e.g.drones, and aerospace, aviation and military applications, and thelike).

Carbon fibers can be made of polyacrylonitrile (PAN), pitch, basalt andthe like. Among all carbon fibers, PAN-based carbon fibers are the mostpopular products. The PAN-based carbon fibers have a variety of tensilestrength and/or high modulus, and all the products available on themarket are provided in specific specifications. This results in variouslimitations of the applications of these high-performance fibers.

Carbon fibers are often offered as carbon fiber tows, and theirspecifications are decided by the number of carbon filaments containedtherein. For example, a 3K carbon fiber tow refers to the carbon fibertow that contains 3000 carbon filaments, while a 12K carbon fiber towrefers to the carbon fiber tow that contains 12000 carbon filaments.

Carbon fiber tows are essential for composite materials used in pioneertechnologies. The raw material of carbon fiber tows needs to beprocessed by oxidation, high-temperature (e.g. 1280° C.) carbonization,etc. in a route more than 900 meters so as to produce black carbonfilaments having high tensile strength and/or high modulus. Since theprocess includes passing the raw material through a series of guiderollers and more than twelve tension devices, the process is onlysuitable for large carbon fiber tows which have a large number of carbonfilaments (e.g. 36000 carbon filaments or more, such as 36K, 48K, 50K,60K or higher). In contrast, for small carbon fiber tows which have asmall number of carbon filaments (e.g. 24000 carbon filaments or less,such as 24K, 12K, 6K, 3K or 1K), the above-mentioned process cannot beused because the small carbon fiber tows are prone to be broken duringthe process, so an alternative method with a shorter route for oxidationand/or carbonization is needed. Therefore, the tensile strength and/ormodulus of a small carbon fiber tow are usually less than those of alarge carbon fiber tow. In addition, the small carbon fiber towsavailable on the market have a much shorter length than the large carbonfiber tows (e.g. 2400 meters for 1K, 3K carbon fiber tows) because ofthe processing difficulties, and this is disadvantageous for costreduction.

In the products of Toray, a famous carbon fiber manufacturer, thespecifications of carbon fiber tows with different tensile strength areobviously different. For 1K carbon fiber tows, the only product providedis made of T300 which has the lowest tensile strength; and for 3K carbonfiber tows, the only products are made of T300 or T400 series which havelower tensile strength. As for products of T700 or T1100 series whichhave higher tensile strength, only 12K or 24K carbon fiber tows can befound, and no 1K or 3K carbon fiber tows are offered for sale.Similarly, for Toray products of M35 to M55 series which have highermodulus and higher tensile strength, only 6K or 12K products can befound, and no 1K or 3K products are offered for sale. Because thediameters of 1K and 3K carbon fiber tows are smaller than those of 12Kand 24K carbon fiber tows, 1K and 3K carbon fiber tows can be used toproduce carbon fiber fabric with finer texture and various patterns.However, the tensile strength of 1K and 3K carbon fiber tows is lower inthe commercially available products. In the case of using small carbonfiber tows (e.g. having 1000 to 6000 carbon filaments), multiple layersof carbon fiber fabrics are required to increase the structural strengthof the product, resulting in not only increased weight and/or thickness,but also increased cost of the production. Therefore, in order tosimultaneously improve the tensile strength and/or modulus of carbonfiber fabrics and reduce the thickness and weight of the product, it isnecessary to develop a method for manufacturing small carbon fiber tows(e.g. having 1000 to 3000 carbon filaments) with high tensile strengthand/or modulus so as to produce lighter, smaller products with higherstructural strength and flexural rigidity, thus achieving the purpose ofenergy saving and carbon reduction.

In addition, the price of carbon fiber tows is inversely proportional tothe size of carbon fiber tows. That is, 1K, 3K, and 6K carbon fiber towsare more expensive than 12K, 24K carbon fiber tows or carbon fiber towscontaining more carbon filaments. Therefore, it is necessary to developa low cost method to obtain 1K, 3K, and 6K carbon fiber tows.

Moreover, 2K, 4K, and 5K carbon fiber tows are not commerciallyavailable. In order to diversify the pattern of woven fabric made ofcarbon fiber tows, it is necessary to develop a method to produce thecarbon fiber tows in these sizes.

SUMMARY OF THE INVENTION

To overcome the shortcomings, one of the objectives of the presentinvention is to develop a method for producing a small carbon fiber tow(e.g. having 1000 to 3000 carbon filaments) with high tensile strengthand/or high modulus. Products produced from the small carbon fiber towsof the present invention are lighter but stronger than the products madeof commercially available small carbon fiber tows, so as to reduce theamount of raw materials (carbon fiber tows) and achieve the purpose ofenergy saving and carbon reduction.

Another objective of the present invention is to develop a method toreduce the cost of manufacturing a small carbon fiber tow (e.g. having1000 to 3000 carbon filaments) with high tensile strength (e.g. having atensile strength of 4500 MPa or higher), or with high modulus and hightensile strength (e.g. having a modulus of 300 or higher and a tensilestrength of 4000 MPa or higher).

Another objective of the present invention is to manufacture carbonfiber tows in a specification not commercially offered for sale, such as2K, 4K and 5K.

To achieve the aforementioned objectives, the present invention providesa method for splitting a carbon fiber tow, which comprises the followingsteps: (A) providing a carbon fiber tow comprising multiple carbonfilaments sized with a solution containing a first sizing material; (B)passing the carbon fiber tow through a first heating device to heat thecarbon fiber tow at a temperature of between 45° C. and 140° C., so asto soften the first sizing material and form a spread carbon fiber tow;(C) adjusting the tension of the spread carbon fiber tow; (D) passingthe spread carbon fiber tow through at least one splitter to obtain aplurality of multiple carbon fiber strands spaced apart; (E) passing thespread carbon fiber tow through at least one cutter to cut the carbonfilaments connected between the carbon fiber strands; (F) adjusting thetension of the carbon fiber strands; (G) sizing the carbon fiber strandswith a solution containing a second sizing material to obtain multiplesized carbon fiber strands; and (H) passing the multiple sized carbonfiber strands through a second heating device to heat the sized carbonfiber strands.

With the method for splitting a carbon fiber tow of the presentinvention, a larger carbon fiber tow (e.g. having more than 12000 carbonfilaments) can be used to produce multiple smaller carbon fiber tows(e.g. having 1000 to 6000 carbon filaments), wherein the plurality ofthe small carbon fiber tows produced by the method of the presentinvention has better tensile strength and/or modulus than thecommercially available equivalents having the same number of carbonfilaments. Since the commercially available small carbon fiber tows areexpensive, the method of the present invention provides small carbonfiber tows of better quality and at lower cost.

In addition, the method for splitting a carbon fiber tow of the presentinvention can produce carbon fiber tows containing a number of carbonfilaments which are not yet commercially offered. For example, a 12Kcarbon fiber tow can be used to produce six 2K carbon fiber tows withfive splitters; a 50K carbon fiber tow can be used to produce ten 5Kcarbon fiber tows with nine splitters; and a 60K carbon fiber tow can beused to produce fifteen 4K carbon fiber tows with fourteen splitters.

In some embodiments of the present invention, the spread carbon fibertow has a maximum width for the carbon fiber tow. In some embodiments ofthe present invention, the maximum width for the carbon fiber tow is themaximum width that a carbon fiber tow can reach while the spread carbonfiber tow has an even top surface or a consistent thickness. The maximumwidth may vary because of the source of the carbon fiber tows. Forexample, the maximum width of 12K carbon fiber tows can be 16 mm to 20mm, such as 18 mm to 20 mm. The maximum width of 24K carbon fiber towscan be 32 mm to 40 mm, such as 36 mm to 40 mm. The maximum width of 48Kcarbon fiber tows can be 60 mm to 68 mm. The maximum width of 50K carbonfiber tows can be 70 mm to 80 mm. The maximum width of 60K carbon fibertows can be 80 mm to 100 mm, such as 90 mm to 100 mm.

In some embodiments of the present invention, the step (B) can berepeated multiple times to obtain the spread carbon fiber tow. In someembodiments of the present invention, the step (B) can be repeatedmultiple times for the carbon fiber tow having 24000 to 60000 carbonfilaments (e.g., 24K, 36K, 48K, 60K) to make the spread carbon fiber towhas a maximum width for the carbon fiber tow. In some embodiments of thepresent invention, the step (B) can be repeated twice or more. In someembodiments of the present invention, the step (B) can be repeated threetimes or more.

In some embodiments of the present invention, when the step (B) isrepeated multiple times, the carbon fiber tow stands still for a periodof time between each step (B). In some embodiments of the presentinvention, the carbon fiber tow stands still until the carbon fiber towcools down.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises adjustingthe tension of the carbon fiber tow after the step (A) and before thestep (B).

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises, in the step(H), passing the multiple sized carbon fiber strands through a coolingdevice after passing the multiple sized carbon fiber strands through asecond heating device.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises adjustingthe width of the multiple sized carbon fiber tows. In some embodimentsof the present invention, the method for splitting a carbon fiber tow ofthe present invention further comprises adjusting the width of themultiple sized carbon fiber tows.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises adjustingthe tension of the carbon fiber strands after passing the multiple sizedcarbon fiber strands through a second heating device and beforeadjusting the width of the multiple sized carbon fiber tows.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises adjustingthe tension of the carbon fiber strands after passing the multiple sizedcarbon fiber strands through a cooling device and before adjusting thewidth of the multiple sized carbon fiber tows.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises adjustingthe tension of the multiple sized carbon fiber strands after passing themultiple sized carbon fiber strands through a second heating device andbefore passing the multiple sized carbon fiber strands through a coolingdevice.

In some embodiments of the present invention, the method for splitting acarbon fiber tow of the present invention further comprises, after thestep (E) and before the step (F), guiding each of the carbon fiberstrands to one of guiding rollers respectively, wherein any two adjacentcarbon fiber strands were guided to guiding rollers at different heightlevel.

In some embodiments of the present invention, the first sizing materialand the second sizing material are the same or different. In someembodiments of the present invention, the concentrations of first sizingmaterial and the second sizing material can be 0.8%, 1.0% or 1.2%.

In some embodiments of the present invention, the first sizing materialis a thermosetting material.

In some embodiments of the present invention, the second sizing materialcomprises a thermoplastic material or a thermosetting material.

In some embodiments of the present invention, when the first sizingmaterial and/or the second sizing material are a thermosetting material,the solution containing first sizing material or the second sizingmaterial substantively does not comprise any curing agent. In someembodiments of the present invention, the solution containing firstsizing material or the second sizing material comprises one or moresurfactants.

In some embodiments of the present invention, the second sizing materialcomprises a thermoplastic material. In some embodiments of the presentinvention, when the second sizing material comprises a thermoplasticmaterial, a cooling step is needed after the step (H), that is, passingthe multiple sized carbon fiber strands through a cooling device. Insome embodiments of the present invention, the thermoplastic material isselected from a group consisting of an acrylonitrile butadiene styrene(ABS), a polypropylene (PP), a polyethylene (PE), a polycarbonate (PC),a polyurethane (PU), a polystyrene (PS), a polyethylene terephthalate(PET), and a polyetheretherketone (PEEK).

In some embodiments of the present invention, the second sizing materialcomprises a thermosetting material. In some embodiments of the presentinvention, the thermosetting material is an epoxy resin.

In some embodiments of the present invention, the carbon fiber tow isheated at a temperature of between 80° C. and 120° C. in Step (B).

In some embodiments of the present invention, the multiple sized carbonfiber strands are heated at a temperature of between 80° C. and 120° C.in Step (H).

In some embodiments of the present invention, after the step (H), themultiple sized carbon fiber strands are cooled at a temperature ofbetween 2° C. and 10° C.

In some embodiments of the present invention, the at least one splittermay be made of metal.

In some embodiments of the present invention, each splitter contains apointed end, in which each pointed end contacts the spread carbon fibertow first to split the spread carbon fiber tow into multiple carbonfiber strands spaced apart.

In some embodiments of the present invention, the at least one splitteris configured to equally split the spread carbon fiber tow into multiplecarbon fiber strands spaced apart. In some embodiments of the presentinvention, the at least one splitter is configured to split the spreadcarbon fiber tow into multiple carbon fiber strands spaced apart in aninequal manner.

In some embodiments of the present invention, the carbon filamentsconnected between the carbon fiber strands were cut by at least onecutter. In some embodiments of the present invention, the at least onecutter may be made of metal, such as tungsten steel, titanium, orsilicon carbide (carborundum). In some embodiments of the presentinvention, the at least one cutter is a circular blade, such as, acircular saw blade.

In some embodiments of the present invention, the splitters and thecutters are correspondingly arranged. In some embodiments of the presentinvention, the number of the splitters and the number of the cutters arethe same.

In some embodiments of the present invention, the carbon fiber tow ispassed through the first heating device at a speed of 8 meters perminute (m/min) to 15 m/min.

In some embodiments of the present invention, the spread carbon fibertow is passed through the at least one splitter at a speed of 8 m/min to15 m/min.

In some embodiments of the present invention, the split carbon fibertows have a breaking strength of 16.0 kgf or higher and a breakingelongation of 4.8% or higher.

In some embodiments of the present invention, the split carbon fibertows have a tensile strength of 4500 million pascals (MPa) or higher,5000 MPa or higher, 5500 MPa or higher, 6000 MPa or higher, or 7000 MPaor higher; while each of the split carbon fiber tows contains 3000carbon filaments or less, 2000 carbon filaments or less, or 1000 carbonfilaments or less.

In some embodiments of the present invention, the split carbon fibertows have a modulus of 300 gigapascals (GPa) or higher, or 350 GPa orhigher, or 400 GPa or higher, or 450 GPa or higher, or 500 GPa orhigher, or 540 GPa or higher; and a tensile strength of 4000 MPa orhigher, 4100 MPa or higher, 4200 MPa or higher, 4300 MPa or higher, 4400MPa or higher, 4500 MPa or higher, 4600 MPa or higher, or 4700 MPa orhigher; while each of the split carbon fiber tows contains 3000 carbonfilaments or less, 2000 carbon filaments or less, or 1000 carbonfilaments or less. In some embodiments of the present invention, thesplit carbon fiber tows also have a modulus of 550 GPa or lower, or 600GPa or lower.

In some embodiments of the present invention, the split carbon fibertows have a length of about 5000 meters. In the context, the term“about” means represents ±3% of the measured value. The length of thesplit carbon fiber tows is equal to the original carbon fiber tow.Therefore, the split carbon fiber tows have a much longer length (abouttwice longer) than those small carbon fiber tows available on themarket.

Other objectives, advantages and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a carbon fiber tow wound on a bobbin;

FIG. 2 is a schematic diagram showing the spreading of the carbon fibertow;

FIG. 3 is a schematic diagram of guide roller assemblies;

FIG. 4 is a schematic diagram of a spread carbon fiber tow wound on abobbin;

FIG. 5 is a schematic diagram showing the splitting and subsequenttreatment of the carbon fiber tow;

FIG. 6 is a schematic diagram of a guide roller with eight grooves;

FIG. 7 is a schematic diagram of the carbon fiber tow produced by themethod of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example is exemplified below to illustrate the implementation of themethod for splitting a carbon fiber tow of the present invention. Aperson skilled in the art can easily realize the advantages and effectsof the present invention in accordance with the example and theaccompanied drawings. It should be understood that the descriptionsproposed herein are just preferable embodiments for the purpose ofillustration only, not intended to limit the scope of the presentinvention. Various modifications and variations can be made to thepresent invention, without departing from the spirit and scope of theinvention.

Example

As shown in FIG. 1 , a commercial PAN carbon fiber tow 1 (manufacturer:Toray Industries, Inc., Japan; product no.: T700SC) having a width ofW1, which was wound on a bobbin, was provided. The carbon fiber tow 1had a length of 5000 meters (m) and a width (W1) of 7 millimeters (mm).The carbon fiber tow 1 contained 12000 carbon filaments (e.g. 12K), andwas sized with an epoxy resin. In the following example, the 12K carbonfiber tow 1 was equally split and further sized into four split carbonfiber tows 21 by the method of the present invention, wherein each ofthe split carbon fiber tows 21 had a length of 5000 m and contained 3000carbon filaments (e.g. 3K).

In the method of the present invention, the carbon fiber tow 1 wasspread, split, and sized. The carbon fiber tow 1 was unwound and heatedto be spread; the spread carbon fiber tow 7 was wound for further usefirst, and then unwound to be split and sized. The tension of the carbonfiber tow 1, the spread carbon fiber tow 7 and the split carbon fibertows 21 was adjusted between steps for many times. The whole productionline in the example is about 15 meters (m), and two spread carbon fibertows 7 can be split at the same time to obtain eight split carbon fibertows 21 because all rollers are wide enough to accommodate the tows andstrands. The process was described in detail below.

First of all, an additional segment of sub-quality carbon fiber tow wasstuck to the end of the carbon fiber tow 1 as a first guiding tow (notshown) by super glue. As shown in FIG. 2 , the commercial carbon fibertow 1 glued with the first guiding tow was provided on a feed creel 2.The free end of the first guiding tow was guided by hand from the feedcreel 2 through a direction adjuster 3 to a tension device 4A first, andguided to a series of guide rollers 5 including a first guide roller 5A,multiple guide roller assemblies 5B and a second guide roller 5C. Thefeed creel 2 could regulate the tension of the carbon fiber tow 1 sothat the carbon fiber tow 1 left the feed creel 2 with a constanttension. The direction adjuster 3 enabled the carbon fiber tow 1 to gostraight to the tension device 4A and the series of guide rollers 5. Thetension device 4A regulated the tension of the carbon fiber tow 1 beforespreading, so that the carbon fiber tow 1 was not too tight, or tooslack and sagged.

While the carbon fiber tow 1 arrived at the section between the firstguide roller 5A and the second guide roller 5C, the carbon fiber tow 1was guided to pass through an infrared heater 6 and heated at atemperature between 80° C. and 120° C., so as to soften the epoxy resinthat sized the carbon fiber tow 1. As a result, the width of the carbonfiber tow 1 was gradually increased, as the tow schematicallyillustrated below between the two dashed lines in FIG. 2 . Each of theplurality of guide roller assemblies 5B comprised a guide roller 51 anda track 52, as shown in FIG. 3 . The position of the guide roller 51 wasadjustable along the track 52 so as to adjust the route length of thecarbon fiber tow 1 between the first guide roller 5A and the secondguide roller 5C. As the vertical distance between two guide rollers 51in adjacent guide roller assemblies 5B increased, the route length ofthe carbon fiber tow 1 increased, so that the heating time could beadjusted to sufficiently soften the epoxy resin that sized the carbonfiber tow 1. In order to further increase the heating time, the numberof the plurality of guide roller assemblies 5B could be increased, whichresulted in a longer route length of the carbon fiber tow 1. In thisexample, the number of the plurality of guide roller assemblies 5B isfive; in other embodiments, the number of the plurality of guide rollerassemblies 5B may be from four to twelve. In this example, the adjacentguide roller assemblies 5B are positioned at different height levels; inother embodiments, all guide roller assemblies 5B may be positioned atthe same height level.

When the carbon fiber tow 1 was guided out of the second guide roller5C, the 12K carbon fiber tow 1 had been spread into the spread carbonfiber tow 7 having a width (W2) of 16 mm. The tension of the spreadcarbon fiber tow 7 was further regulated by the tension device 4B, sothat the spread carbon fiber tow 7 was not too tight, or too slack andsagged. After that, the spread carbon fiber tow 7 was further guided toa first winder 8. When the free end of the first guiding tow arrived atthe first winder 8, the joint of the first guiding tow and the spreadcarbon fiber tow 7 left the feed creel 2. At this point, the firstwinder 8 started to operate at a winding speed of 25 meters per minute(m/min) so that the carbon fiber tow 1 was left the feed creel 2 at thesame speed. Therefore, the feeding speed could be controlled by thefirst winder 8. When the spread carbon fiber tow 7 started to be woundon first the winder 8, the first guiding tow was removed. As shown inFIG. 4 , the spread carbon fiber tow 7 having a width of W2 was wound ona bobbin. It is noted that W2 is larger than W1.

Similarly, an additional segment of sub-quality spread carbon fiber towwas stuck to the end of the spread carbon fiber tow 7 as a secondguiding tow (not shown in figures) by super glue.

As shown in FIG. 5 , a spread carbon fiber tow 7 was provided on a feedcreel 9. In this example, two spread carbon fiber tows 7 spaced apartwere provided in parallel to enhance product yield.

The free end of each second guiding tow was guided by hand to a tensiondevice 10. The tension device 10 regulated the tension of each spreadcarbon fiber tow 7 so that the spread carbon fiber tows 7 were not tootight, or too slack and sagged.

Subsequently, the free end of each second guiding tow was guided by handto a splitting device 11. In this example, the splitting device 11comprised two sets of splitters 11A, wherein each of the sets containedthree evenly spaced splitters 11A. The six splitters 11A were arrangedon a hypothetical straight line perpendicular to the moving direction ofthe carbon fiber tows. When each spread carbon fiber tow 7 passedthrough one set of the splitters 11A, the spread carbon fiber tows 7having 12000 carbon filaments were equally divided into four carbonfiber strands 20, each of which contained 3000 carbon filaments and hada width of 4 mm. The eight carbon fiber strands 20 were guided to eightgrooves G on a first grooved guiding roller 11B and then to eightcorresponding grooves G on a second grooved guiding roller 11D. Eachgroove G had a width of 4 mm, and the distance between two adjacentgrooves G was 2 mm. The rollers arranged after the first grooved guidingroller 11B contained the same number of grooves G to accommodate theeight carbon fiber strands 20.

Since the carbon filaments comprised in the spread carbon fiber tows 7might be skewed, not kept completely straight in the whole spread carbonfiber tows 7, there were carbon filaments connected between the carbonfiber strands 20 after splitting by the splitters 11A. Six cutters 11Cwere arranged on a hypothetical straight line perpendicular to themoving direction of the carbon fiber strands 20 between the firstgrooved guiding roller 11B and second grooved guiding roller 11D, to cutthe carbon filaments connected between the carbon fiber strands 20.

After the second grooved guiding roller 11D, the eight carbon fiberstrands 20 were then guided by hand to a third grooved guiding roller11E, which also had eight grooves G as the first grooved guiding roller11B, and arranged at a lower height level than the first grooved guidingroller 11B and second grooved guiding roller 11D. The difference ofheight level was advantageous to evenly transport the carbon fiberstrands 20. FIG. 6 schematically shows the guide roller 11B which haseight grooves G. The first grooved guiding roller 11B, second groovedguiding roller 11D and third grooved guiding roller 11E contained thesame number of grooves G to accommodate the carbon fiber strands 20.

The carbon fiber strands 20 were then sequentially guided to two sets ofguide rollers 11F, wherein each set contained four guide rollers 11F atdifferent height levels. Each of the carbon fiber strands 20 was guidedto one of the guide rollers 11F to expand the distance between any oftwo adjacent carbon fiber strands 20. Any two adjacent guide rollers 11Fwere space apart by a vertical distance of 10 cm. Guide rollers 11F werenot grooved. The horizontal distance between two carbon fiber strands 20on two adjacent guide rollers 11F was about 5 mm. Therefore, the carbonfiber strands 20 are vertically and horizontally spaced apart.

The eight carbon fiber strands 20 were guided to a tension device 12.The route lengths of the carbon fiber strands 19 were different, so thetension device 12 was arranged to regulate the tension of the eightcarbon fiber strands 20 so that the carbon fiber strands 20 were not tootight, or too slack and sagged. Since the carbon fiber strands 20 weresplit, cut and spaced apart with appropriate vertical and horizontaldistances.

Subsequently, the eight carbon fiber strands 20 were then sized, heatedand cooled.

After the tension device 12, the eight carbon fiber strands 20 wereguided to a sizing device 13, which comprised a sizing bath 13A, agrooved guide roller 13B, a grooved guide roller 13C, and a roller 13D.The grooved guide roller 13B and the grooved guide roller 13C were madeof stainless steel while the roller 13D was made of synthetic rubber. Inthis example, the sizing bath 13A was filled with a thermoplastic slurrycomprising acrylonitrile butadiene styrene (ABS) polymer. The ABSpolymer was dissolved in water to obtain the sizing solution with sizingcontent of 1%. After the eight carbon fiber strands 20 were guidedthrough the sizing bath 13A, each of the eight carbon fiber strands 20was sized with the sizing solution so as to eliminate carbon fiber fuzzand thus smooth the surfaces of the eight carbon fiber strands 20. Whenthe eight carbon fiber strands 20 were guided through the grooved guideroller 13C, these carbon fiber strands 20 were pressed by the roller 13Din order to squeeze extra sizing solution. Eight carbon fiber strands 20were sized.

Subsequently, the eight carbon fiber strands 20 were guided to a heatingdevice 14, which comprised multiple grooved guide rollers 14A andmultiple infrared heaters 14B. The temperature of the plurality ofinfrared heaters 14B was set between 120° C. and 140° C. so as toevaporate the water in the eight carbon fiber strands 20. The eightcarbon fiber strands 20 were then guided to a tension device 15 toadjust the tension of the eight carbon fiber strands 20.

The eight carbon fiber strands 20 were then guided to a cooling chamber16, which contained multiple grooved guide rollers 16A. The temperatureof the cooling chamber 16 was set between 3° C. and 7° C. to cool theeight carbon fiber strands 20 and facilitate the cure of thethermoplastic sizing material (e.g. ABS polymer). The eight carbon fiberstrands 20 were then guided to a tension device 17 to adjust the tensionof the eight carbon fiber strands 20. After that, eight split carbonfiber tows 21 were obtained. The eight carbon fiber tows 21 could beoptionally guided by hand to grooved roller 18 to adjust the width ofthe sized carbon fiber tows 21. The width of the grooves on the groovedroller 18 was 2.9 mm. After the width adjustment, the width of the eightsplit carbon fiber tows 21 was adjusted to 2.9 mm (W3). When the widthof the split carbon fiber tows 21 was not adjusted, the grooves on thegrooved roller 18 could be removed or replaced by another roller withoutgrooves for width adjustment.

When the eight free ends of the split second guiding tows arrived at theeight winders 19A in a winding device 19, the winding device 19 startedto operate at a winding speed of 12.5 m/min to pull the two spreadcarbon fiber tows 7. Therefore, the feeding speed of the spread carbonfiber tows 7 could be controlled by the winding device 19. After thestrands split from the second guiding tows were totally wound, thesecond guiding tows were removed and the split carbon fiber tows 21after the second guiding tows were wound. As shown in FIG. 7 , the splitcarbon fiber tows 21 having a width of W3 were wound on a bobbin. Asabove, the width adjustment step is optional, and the split carbon fibertows 21 without width adjustment had a width of W3′ (not shown). It isnoted that W3 and W3′ are both smaller than W1, and W3 is smaller thanW3′. In this example, there were eight split carbon fiber tows 21produced from the two spread carbon fiber tows 7, wherein each of thecarbon fiber tows 21 had a length of 5000 m and contained 3000 carbonfilaments (e.g. 3K). In addition, the length of the eight split carbonfiber tows 21 was the same as that of the carbon fiber tow 1.

Test Example: Breaking Strength and Breaking Elongation of Produced 3KCarbon Fiber Tow

In this test example, a section of the carbon fiber strands 21 withoutwidth adjustment, which had a width of 4 mm, was used as a test sample.

Breaking strength and breaking elongation of the test sample weremeasured in accordance with ASTM D2256-2002, Option A1, wherein the testsample was loaded into grips, the gage length (length of thread betweengrips) was 25 cm, and the speed of testing was 30±1 centimeters perminute (cm/min).

For the test sample, the breaking strength was 16.0 kilogram-force (kgf)and the breaking elongation was 4.8%. From comparison of breakingstrength and breaking elongation with the control test samples, it isfound the test sample is the equivalent of T500 and T550 of the carbonfiber tow produced by Toray Industries, Inc.

With the method for splitting a carbon fiber tow of the presentinvention, a commercial 12K PAN carbon fiber tow, which has bettertensile strength than other commercially available 3K carbon fiber tow,can be used to produce four 3K carbon fiber tows. The 3K carbon fibertows obtained by splitting the 12K PAN carbon fiber tow have bettertensile strength than other commercially available 3K carbon fiber tows.From the above description, a small carbon fiber tow (e.g. 1K to 6K)with higher tensile strength or modulus can be produced by the methodfor splitting a carbon fiber tow of the present invention. Thus, theproducts manufactured from the small carbon fiber tow obtained by thepresent invention have enhanced strength, and can be applied to manyother technical fields.

In summary, the method for splitting a carbon fiber tow of the presentinvention can provide small carbon fiber tows (e.g. having 1000 to 6000carbon filaments) with increased tensile strength and/or modulus thancorresponding commercial products, and reduce the production costthereof. The split carbon fiber tows produced by the present inventioncan be applied to many a variety of products, such as 3C products,sporting goods, wind power generation, new energy vehicles, drones,aerospace, aviation and military applications, and the like, and theycan also be used as the raw material for 3D printing. The productsproduced from the small carbon fiber tows obtained by the presentinvention are lighter but stronger.

Even though numerous characteristics and advantages of the presentinvention have been set forth in the foregoing description, togetherwith details of the features of the invention, the disclosure isillustrative only. Changes may be made in the details, especially inmatters of shape, size, and arrangement of parts within the principlesof the invention to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed.

What is claimed is:
 1. A method for splitting a carbon fiber tow,comprising: (A) providing a carbon fiber tow comprising multiple carbonfilaments sized with a solution containing a first sizing material; (B)passing the carbon fiber tow through a first heating device to heat thecarbon fiber tow at a temperature of between 45° C. and 140° C., so asto soften the first sizing material and form a spread carbon fiber tow;(C) adjusting the tension of the spread carbon fiber tow; (D) passingthe spread carbon fiber tow through at least one splitter to obtain aplurality of multiple carbon fiber strands spaced apart; (E) passing thespread carbon fiber tow through at least one cutter to cut the carbonfilaments connected between the carbon fiber strands; (F) adjusting thetension of the carbon fiber strands; (G) sizing the carbon fiber strandswith a solution containing a second sizing material to obtain multiplesized carbon fiber strands; and (H) passing the multiple sized carbonfiber strands through a second heating device to heat the sized carbonfiber strands to obtain multiple split carbon fiber tows.
 2. The methodas claimed in claim 1, wherein the spread carbon fiber tow has a maximumwidth for the carbon fiber tow.
 3. The method as claimed in claim 1, thestep (B) is repeated multiple times to obtain the spread carbon fibertow.
 4. The method as claimed in claim 1, further comprising, in thestep (H), passing the multiple sized carbon fiber strands through acooling device after passing the multiple sized carbon fiber strandsthrough a second heating device.
 5. The method as claimed in claim 1,further comprising adjusting the width of the multiple sized carbonfiber tows.
 6. The method as claimed in claim 4, further comprisingadjusting the width of the multiple sized carbon fiber tows.
 7. Themethod as claimed in claim 1, further comprising, after the step (E) andbefore the step (F), guiding each of the carbon fiber strands to one ofguiding rollers respectively, wherein any two adjacent carbon fiberstrands were guided to guiding rollers at different height level.
 8. Themethod as claimed in claim 1, wherein the first sizing material is athermosetting material.
 9. The method as claimed in claim 1, wherein thesecond sizing material comprises a thermoplastic material or athermosetting material.
 10. The method as claimed in claim 9, whereinthe thermoplastic material is selected from a group consisting of anacrylonitrile butadiene styrene (ABS), a polypropylene (PP), apolyethylene (PE), a polycarbonate (PC), a polyurethane (PU), apolystyrene (PS), a polyethylene terephthalate (PET), and apolyetheretherketone (PEEK).
 11. The method as claimed in claim 9,wherein the thermosetting material is an epoxy resin.
 12. The method asclaimed in claim 1, wherein the carbon fiber tow is heated at atemperature of between 80° C. and 120° C. in Step (B).
 13. The method asclaimed in claim 1, wherein the multiple sized carbon fiber strands areheated at a temperature of between 80° C. and 120° C. in Step (H). 14.The method as claimed in claim 4, wherein the multiple sized carbonfiber strands are cooled at a temperature of between 2° C. and 10° C.15. The method as claimed in claim 6, wherein the multiple sized carbonfiber strands are cooled at a temperature of between 2° C. and 10° C.16. The method as claimed in claim 1, wherein the at least one splitteris made of metal.
 17. The method as claimed in claim 1, wherein the atleast one splitter is configured to equally split the spread carbonfiber tow.
 18. The method as claimed in claim 1, wherein the at leastone cutter is a circular saw blade.
 19. The method as claimed in claim1, wherein the split carbon fiber tow has a breaking strength of 16.0kgf or higher and a breaking elongation of 4.8% or higher.
 20. Themethod as claimed in claim 19, wherein the split carbon fiber tow has alength of about 5000 meters.